Network controller with reconfigurable program logic circuits capable of performing both channel sevice and testing functions

ABSTRACT

A network controller card having a processor, memory and program logic. The program logic can be used as communications circuits and as testing circuits. A reconfigure signal from a workstation remotely located from the network controller card initiates the processor to change the program logic from communications circuits to testing circuits and vice versa.

RELATED PATENTS

This patent stems from a continuation application of U.S. patentapplication Ser. No. 08/468,132, filed Jun. 6, 1995, entitled NETWORKCONTROLLER WITH RECONFIGURABLE PROGRAM LOGIC CIRCUITS CAPABLE OFPERFORMING BOTH CHANNEL SERVICE AND TESTING FUNCTIONS, now U.S. Pat. No.5,613,061, which is a continuation application of U.S. patentapplication having Ser. No. 08/304,202, filed Sep. 12, 1994, nowabandoned. The benefit of the earlier filing date of the parent patentapplications is claimed for common subject matter pursuant to 35 U.S.C.§ 120.

BACKGROUND OF THE INVENTION

This invention relates to channel service units and access multiplexers,and more particularly to reconfiguring channel service units and accessmultiplexers as test equipment for testing communication channelsbetween a network and the channel service unit or access multiplexer, orbetween customer premise equipment and the channel service unit andaccess multiplexer.

DESCRIPTION OF THE RELEVANT ART

Channel service units and access multiplexers are well known in the art.An access multiplexer may interface customer premise equipment, such asa local area network, private branch exchange, or other equipment, witha larger area network. The access multiplexer typically formats thecustomer signal to a T1, T3, or other format used over the large areanetwork. A channel service unit similarly performs a formatting functionnecessary to meet certain communication system requirements.

Traditional testing methodology includes hardware test sets andpersonal-computer-based software/hardware test systems. The hardwaretest sets are well known to be portable and rugged, as individual piecesof equipment. The hardware test sets may require a specialized interfacefor each type of testing.

Alternatively, the hardware test sets may provide multiple interfacesfor several types of testing. Often the hardware test sets are equippedwith communications capability to enable remote control by a dumbterminal or software running on a personal computer. The software on thepersonal computer is for controlling the hardware set and is typicallynot part of the test capability.

Hardware test sets are costly, with prices ranging at the current marketrate between one thousand to over fifty thousand dollars. In addition,for remote testing, the hardware test sets require a separatecommunications facility. The high cost and facility requirements createa problem in that the capital investment is not put to work sincetesting is only performed during installation or when something breaks.Additionally, specialized hardware interfaces are redundant, since theaccess multiplexer equipment or channel service unit are alreadyprewired into a circuit which provides an interface for normalcommunications, and this interface is the same as would be used fornormal testing. Personal computers using software to control hardwaretest systems have advanced the art by allowing the personal computer toremotely control a hardware test set. However, these types of systemsstill require specialized hardware interfaces for each type of line orequipment. The interfaces may be in the form of an expansion bus cardwhich goes into the personal computer or may be an external box whichcommunicates with the personal computer via a serial or parallel port.High speed data analysis functions are part of this hardware, but somelow speed functions may be performed in software alone.

The personal-computer-based software/hardware test systems typicallyhave a better "human interface" capability than do traditional hardwaretest sets, not being limited to the fixed switches and light emittingdiode (LED) readouts of a hardware test set system. Instead, graphicaluser interface (GUI) and Windows displays are common.

The personal-computer-based software/hardware test systems often allowusers to create customized displays or test sequences to fit aspecialized need. With few exceptions, however, remote testing requiresspecialized hardware interfaces at all locations where testing may berequired or desirable. These systems typically have a high cost, involvespecialized hardware interfaces which are redundant, require a separatecommunications facility, and result in capital investment which is notput to work. If the remote testing were done with remote test equipment,then a switching matrix, and an appropriate interface for each type ofchannel, would be required to switch the remote test equipment, andappropriate interface, into the proper circuit. The disadvantages ofthis method and equipment would be high cost of the equipment, includinginstallation, wiring and maintenance of the switching matrix, remotetest equipment and interfaces, lower reliability since all ports wouldbe wired through the switch matrix, and typically only one channel wouldbe capable of being tested at any one time.

SUMMARY OF THE INVENTION

A general object of the invention is having any type of dataterminations available for remote testing from a network control center.

Another object of the invention is to reduce the historical capitalequipment and manpower requirements of performing out-of-service testingon communication circuits and equipment.

An additional object of the invention is to remotely place an in-circuitcommunication analyzer system which can test toward the network ortoward the customer premise equipment.

A further object of the invention is a remote user interface capabilitywhich can remotely operate from locations used to manage thecommunications network.

According to the present invention, as broadly described herein, amethod and system for reconfiguring an access multiplexer/channelservice unit as communications test equipment is provided. The methodand system has a network control unit located at the accessmultiplexer/channel service unit. The network control unit, or networkcontroller card, includes program logic, a processor, and a memory.Remotely located from the access multiplexer/channel service unit is awork station.

The method and system comprise the steps of setting the program logiccircuits as communication circuits for performing as a channel serviceunit and/or as an access multiplexer. Thus, the communication circuitsinitially may be set and perform as a channel service unit and/or accessmultiplexer. The method includes initiating from the work station afirst reconfigure signal. The first reconfigure signal is sent throughthe communications channel to the network control unit, located in theaccess multiplexer/channel service unit. Upon receiving the firstreconfigure signal, the processor reconfigures, using software in thememory, the program logic circuits as testing circuits. The testingcircuits are used for testing the communications channel. Dependent uponthe commands in the reconfigure signal, the program logic circuits maybe reconfigured for testing all the channels or a subset of the channelscoming to the channel service unit or access multiplexer. Thus, theprogram logic circuits, on the one hand, function as an accessmultiplexer and/or channel service unit. The access multiplexer and/orchannel service unit can serve as an interface between many types ofchannels, simultaneously. Upon reconfiguring the program logic circuits,the program logic circuits function as the test equipment for testingthe communications channel. The program logic circuits may bereconfigured for testing a single channel, a subset of all the channels,or all the channels, simultaneously. In the event the program logiccircuits are reconfigured as testing circuits for a subset of thechannels, then the program logic circuits may continue functioning ascommunications circuits for those channels for which the program logiccircuits are not reconfigured.

When testing is complete, the program logic circuits, which were used astesting circuits, may be reconfigured as communications circuits. Thus,the work station can send a second reconfigure signal through thecommunications channel to the network control unit. Upon receiving thesecond reconfigure signal, the processor reconfigures, using software inthe memory, the program logic circuits, which were being used as testingcircuits, as the communications circuits.

Additional objects and advantages of the invention are set forth in partin the description which follows, and in part are obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention also may be realized and attained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate preferred embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 illustrates an access multiplexer connecting customer premiseequipment to a wide area network;

FIG. 2 shows a channel service unit connected between a private branchexchange at customer premise equipment and an access multiplexer in awide area network;

FIG. 3 illustrates the channel service unit of FIG. 2 configured astesting circuits, and the access multiplexer configured as testingcircuits;

FIG. 4 is a block diagram of a network controller card having programlogic, a processor and a non-volatile memory;

FIG. 5 shows a work station connected to the network controller card;

FIG. 6 is a flowchart illustrating the method of the present invention;and

FIG. 7 illustrates a user interface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now is made in detail to the present preferred embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals indicate like elementsthroughout the several views.

In the exemplary arrangement shown in FIG. 1, an access multiplexer 37is connected between customer premise equipment including router 32,video codec 33, private branch exchange (PBX) 34, integrated servicesdigital network (ISDN) 35, and data sets 36. The customer equipment sideof the access multiplexer and the customer premise equipment typicallyare slow speed communications channels. The router 32 is connected to alocal area network (LAN) 31. On the network side, the access multiplexer37 is connected to a wide area network 38, which may be connectedfurther to remote area network A 40 and remote area network B 39.Additionally, a control monitor site 41 is remotely connected to theaccess multiplexer 37. The network side of the access multiplexertypically interfaces to high speed communications channels.

As is well known in the art, the access multiplexer 37 is used to changethe format of data coming from a local area network 31 through router 32using V.35, for example, to a T1 format for transmission over the widearea network 38. Additionally, video codec 33 may have other formatssuch as compressed video at 384 kilobits per second (Kbps) converted toproper T1 format. Furthermore, the access multiplexer 37 can multiplexthe output from the router 32, video codec 33, private branch exchange34, ISDN 35, data sets 36, to the proper formats. The outputs of theaccess multiplexer can be any of T1, T3, OC1-OC12, or other formats. TheOC1-OC12 formats are used with optical cables. The control monitor site41 may be remotely located from the access multiplexer 37. The controlmonitor site 41 monitors and controls the performance of the accessmultiplexer. Similar to an access multiplexer 37, a channel service unitmay be substituted for more limited uses.

As shown in FIG. 2, a channel service unit 51 may interface customerpremise equipment and a network. The channel service unit 51 may convertthe T1 D4 traffic to a format for sending over the wide area network.

A first channel service unit 51 may be located at the customer premiseequipment, shown as a private branch exchange (PBX) 54. A second channelservice unit 53 may be located at customer premise equipment, shown asprivate branch exchange (PBX) 55. The second channel service unit 53,may interface through an access multiplexer 52 to the first channelservice unit 51. The first channel service unit 51, working with thesecond channel service unit 53, also may test the communications linkbetween either channel service unit 51, 53 and the access multiplexer52.

As shown in FIG. 3, program logic circuits within the access multiplexer52, and the program logic circuits within the channel service units 51,53 may be reconfigured as testing circuits. The access multiplexer 52,configured as testing circuits, may be testing with T1, ESF testpatterns with the first channel service unit 51. This allows testing ofthe communications link between the first channel service unit 51 andthe access multiplexer 52. At the same time, the program logic circuitswithin the access multiplexer 52 may continue to operate ascommunications circuits for the communications channel between theaccess multiplexer 52 and the channel service unit 53.

The access multiplexer 52 also may be used for testing between thesecond channel service unit 53 and the access multiplexer 52. For thisscenario, the program logic circuits within the access multiplexer 52and the program logic circuits within the channel service unit 53 arereconfigured as testing circuits. Accordingly, the communications linkbetween the access multiplexer 52 and the channel service unit 53 may betested.

With the passage of time, testing techniques change because of newtesting standards, and changing regulatory requirements. With thepresent invention the entire functionality is soft, and can be readilychanged over time.

The present invention allows one to keep up with changes without havingto go into the test set and make physical changes.

The present invention includes network controller means, which includesprogram-logic means, processor means and memory means. The processormeans is coupled to the program-logic means and the memory means. Theprocessor means also is coupled through a communications link 66 to awork station 67 as shown in FIG. 5.

The program logic means may be configured as test circuits orcommunication circuits. The program-logic means is responsive to theprocessor means, which controls how the program-logic means operates.The software for controlling the processor means is typically stored inthe memory means.

As shown in FIG. 4, the processor means is embodied as a processor 63,the memory means is embodied as a nonvolatile reprogrammable memory 64,and the program-logic means is embodied as program logic circuits 62.The memory means may be embodied as other memory devices, such as diskor programmable read only memory, as is well known in the art. Theprogram logic circuits 62 may include gate array circuits, or othercircuits which are reconfigurable based on commands from the processor.The program logic circuits 62, processor 63 and read only memory 64 arecoupled through bus 65. The processor 63 further is coupled through aback plane bus and, as shown in FIG. 5, through a communications channel66 to the work station 67. The network controller means may be embodiedon a card, such as network controller card 61, which inserts into theback plane of an access multiplexer or channel service unit.

Typically, the program logic circuits 62 operate as communicationcircuits. The communication circuits may function as an accessmultiplexer 37 or channel service unit 51, 53. Thus, the program logiccircuits 62 may substitute for the function of the access multiplexer 37as shown in FIG. 1.

As shown in FIG. 6, according to the method of the present invention,the program logic circuits are set 70 as communication circuits duringnormal use. If testing is not required 71, the system operates 72 usingthe communications circuits. If testing is required 71, the firstreconfigure signal is sent 73 from the workstation to the processor 63.In response to a first reconfigure signal, sent 73 from the work station67 through the communications channel 66 to the processor 63, theprocessor 63 reconfigures 74 the program logic circuits 62 as testingcircuits. While reconfiguring the program logic circuits 62, theprocessor 63 uses software embedded in the nonvolatile reprogrammablememory 64. The processor 63 may reconfigure the program logic circuits62 so that all the communications channels see the program logiccircuits 62 as test circuits, or some of the communications channels seethe program logic circuits 62 as test circuits and other communicationschannels see the program logic circuits 62 as communications circuits.Accordingly, the network controller card 61, located in the accessmultiplexer 37 of FIG. 1, changes the function of the access multiplexerto test circuits, or partially retains the function of the accessmultiplexer 37 as communications circuits and partially changes thefunction of the access multiplexer 37 to test circuits. As testcircuits, the program logic circuits 62 are used to test 76 and supportmeasurement and analysis of errors, T-carriers performance, frequencyand time, alarms, data links, signal LEDS, and alarm LEDS.

When taking error measurements, the test circuits can analyze biterrors, average bit error rate, blocks, average block error rate, blockerror rate and clock slip. When taking T-carrier measurements, the testcircuits can analyze frame errors, average frame error rate, severeframe errors, frame synchronization losses, cyclic redundance code (CRC)errors, average CRC error rate, bipolar violations, average bipolarviolations rate, bipolar rate, and data link FCS error. The performancemeasurements may include available seconds, percent available seconds,unavailable seconds, error free seconds, percent error free seconds,violation free seconds, percent violation free seconds, synchronizationseconds, percent synchronization seconds, severely errored seconds,percent severely errored seconds, violated seconds, percent violatedseconds, severely violated seconds, percent severely violated seconds,degraded minutes, percent degraded minutes, synchronization lossseconds, signal loss seconds and errored seconds.

While performing frequency and time measurements, the testing circuitsmay test T1 transmit frequency, T1 receive frequency, FT1 port transmitfrequency, FT1 port receive frequency, external clock frequency,auxiliary T1 reference line frequency and round trip delay. Alarmmeasurements made by the test circuits include loss of signal, loss ofdata, loss of clock, yellow alarm, all ones, low average density, excesszeros, line code configuration alarm (B8ZS, XBTSI, AMI) and loss ofpower.

The data link analysis which may be conducted by the test circuitsincludes real time display of PRMS, real time display of BOPS, real timedisplay of MOPS, protocol analyzer mode and hex or binary display. Thetesting circuits may also test signal light emitting diodes (LEDs) andalarms LEDs including T1 pulses present, pattern synchronization, framesynchronization, B8ZS coding received, signal loss, pattern loss, frameloss, ones density error, excess zeros, yellow alarm, all ones,controlled slips, and coding mismatch detected (B8ZS vs. AMI).

With such a broad range of capabilities and inherent flexibility, thepresent invention can completely replace physical test sets. Instead ofhaving a physical test set, the access multiplexer is simply transformedfrom a communications configuration to a test circuit which can performthe above functions.

An additional advantage to the present invention is that the system canbe reconfigured as a test set, and the test set is always available ateach data termination for remote testing from the network controlcenter. Thus, the access multiplexer can perform as an interface unit,and then be reconfigured as a test unit remotely at any time. Uponcompletion of the job of serving as a test set, the system, in responseto a second reconfigure signal, can be reconfigured back tocommunication circuits.

Returning to the method steps as illustrated in FIG. 6, when testing iscomplete 75, the processor 63 uses software embedded in the nonvolatilereprogrammable memory 64 to reconfigure the program logic circuits 62.In response to a second reconfigure signal sent 77 from the workstationto the processor through the communications channel, the processor 63reconfigures 78 the program logic circuits 62 to function ascommunication circuits. Accordingly, the network controller card 61,located in the access multiplexer 37 of FIG. 1, changes the function ofthe access multiplexer to communication circuits.

With the program logic circuits 62 operating 72 as communicationscircuits, the system may function as an interface and can be configuredto have the following capabilities: transmit frequency capability,aggregate framing capability, line code capabilities, error insertioncapabilities, interface capabilities, and data link generatorcapabilities.

The transmit frequency capability includes transmit frequencysynthesizer, recovered from receiver line, recovered from separate T1reference line, recovered from FT1 port (n×56 or n×64), external TTL,and external RS422. The transmit frequency synthesizer may perform n×56Kbs, n×64 Kbs, T1 5 (1.544 Mbs), E1 (2.048 Mbs) with a synthesizeradjustable with ±400 Hz in 1 Hz increments.

Aggregate framing capability includes ESF, SF (D2, D3, D4), SLC-96,unframed, and CCITT G.703. Line code capabilities include AMI, B8ZS,HDB3, and ZBTSI. The error insertion capabilities may include singletest pattern logic error, single frame error, single severe frame error,single bipolar violation, and user programmable insertion error rate.The interface capabilities include T1 having a T1 repeater, DSX1 lineinterface with equalizer and bridge monitor or terminate receiver, E1with a 75 ohm unbalanced, FT1 with a 56 Kbs to 1.536 Mbs synchronous inn×56 Kb or n×64 Kb increments.

Asynchronous ports may include RS232D or 1200 baud to 56 Kilobaud. Thedata link generator capabilities may include AT&T type messagegeneration, T1.403 PRM Generation, and user data generation.

The present invention can be placed remotely in circuits anywhere anaccess multiplexer is installed and is configurable to act as a test seteither toward the network or toward the customer premises equipment.Thus, unlike the traditional arrangement in which test equipment must becarried by an individual to the access multiplexer remote location foreach test, with the present invention there is no need to have anindividual go to the remote location to install a test set or to changeits orientation. Rather, the present invention can be remotely installedand operated from any location used to manage the communication network.

The present invention takes advantage of advanced programmablearchitecture to perform in-service and out-of-service testing ofcommunication circuits and equipment. The specific test capabilitiesvary with the specific interface plug to which software has beendownloaded. For example, when downloaded to a T1 channel service unitplug, such as an NCC or TAC, the available tests and user interface areas shown in FIG. 7. If, however, the software were downloaded to amulti-port fractional T1 multiplex plug, then the user interface screenand available tests are specific to data circuit and equipment needs.The appropriate user interface screen is automatically displayed at thework station, based upon the type of plug to which the software isdownloaded. Downloading can be done either remotely or locally.

Using plug-in modularity and advanced programmable architecture, thepresent invention provides a wide range of network applications from asimple T1 channel service unit to up to thirty T1 lines for variousprivate line and switched services. The advanced programmablearchitecture utilizes programmable gate arrays and nonvolatile flashmemory technology to provide a uniquely flexible platform forimplementing change without obsoleting existing hardware. On download ofsoftware from a remote terminal, the programmable gate arrays actuallyalter the circuits of the device. Reprogramming thereby saves the costof replacement hardware and eliminates the allocation of labor and timeassociated with hardware changeouts typical of the traditionalapplication-specific integrated circuit (ASIC) architecture technology.

The present invention may also be embodied as an access multiplexerintegrated DSU/CSU (IDCSU). The IDCSU represents a cost-effective meansof providing a single high-speed data application port and T1 networkinterface on a single module. The integrated, single module capabilityallows a very high density of T1 DSU/CSUs to be deployed at a site, andit features diagnostics, DS0 channelization flexibility, full network T1Extended Superframe (ESF) performance monitoring, and managementcapability.

The IDCSU can be deployed through a field upgrade to existing equipment.Software is loaded to create a single-port T1 DSU/CSU using theidentical hardware modules of the access multiplexer carrier accessmodules. An appropriate connector module is added to provide interfacesto the network and to the Data Terminal Equipment (DTE) or DataCommunications Equipment (DCE) applications.

Integrated high-speed/low-speed modules can be used to provide either ahigh-speed (V.35) or high-speed (RS449) port and a low-speed RS232 portwhen used with the present invention access multiplexer. The low-speedports are designed to be transparent so that in the network they appearlike a direct-connect cable. Because both data and control leads arepassed over the network, control leads used for monitoring of differentunits, e.g., as in an application in which a modem is monitored by apersonal computer, are replaced by the wide area network using theaccess multiplexer. The high speed/low speed capability also applies toco-located high speed and low-speed units, e.g., a high-speed CAD/CAMgraphics terminal networked with a low-speed plotter. Thehigh-speed/low-speed modules also can be used to provide an in-bandmanagement channel between an access multiplexer and access multiplexernodes.

The present invention may also include a 56K data service unit. The 56Kdata service unit allows an access multiplexer to manage remotededicated 56K circuits, performing the following functions:

Monitor DDS control code information per AT&T

Identify and manage alarms on DDS control code

Send 56K loopback signals and test patterns

Monitor circuit data

The 56K is available as an upgrade to an existing plug-in module eitheras a EPROM upgrade or as a software downloadable circuit upgrade. Theresulting plug-in module provides digital dataphone service.

As an advanced programmable architecture option, T1 dial backupcapability can be added to the present invention by downloading softwareto alter the circuits of an existing plug-in module. The T1 dial backupoption, used to backup T1 and FT1 circuits and 56K circuits that havebeen multiplexed onto a T1, provides a cost-effective solution to theproblem of ensuring satisfactory up-time for end users. Expensive, idlededicated circuits are no longer needed for backup capability. The T1dial backup option initiates backup from either end of a circuit in theevent of a failure detected on recognition of T1 loss of frame orabnormal station code. Switching to the backup circuit can occurautomatically or manually, and the failed circuit remains accessible fortroubleshooting.

It will be apparent to those skilled in the art that variousmodifications can be made to the network access system and method of theinstant invention without departing from the scope or spirit of theinvention, and it is intended that the present invention covermodifications and variations of the network access system and methodprovided they come within the scope of the appended claims and theirequivalents.

I claim:
 1. A system for remotely controlling a plurality of channelservice units interfacing between customer equipment and a network andfor remotely reconfiguring the plurality of channel service units tooperate as at least one of a plurality of channel service units and aplurality of test units, the system comprising:a workstation forinitiating reconfigure signals; a communications channel, coupled to theworkstation, for transmitting the reconfigure signals; a first privatebranch exchange; a first channel service unit, operatively coupled tothe communications channel and to the first private branch exchange,said first channel service unit for operating, responsive to thereconfigure signals, as at least one of a test unit and a channelservice unit; a second private branch exchange; a second channel serviceunit, operatively coupled to the communications channel and to thesecond private branch exchange, said second channel service unit foroperating, responsive to the reconfigure signals, as at least one of atest unit and a channel service unit; and an access multiplexer,operatively coupled to said first channel service unit through a firstlink and to said second channel service unit through a second link, formultiplexing signals received from said first channel service unit andfrom said second channel service unit as multiplexed signals and fortransmitting the multiplexed signals over the network.
 2. The system asset forth in claim 1 with said first channel service unit operating as atest unit and testing the first link and said second channel serviceunit operating as a test unit and testing the second link.
 3. The systemas set forth in claim 1 with said access multiplexer configured,responsive to the reconfigure signals, as testing circuits for testingthe first link with T1, ESF test patterns.
 4. The system as set forth inclaim 3 with said access multiplexer simultaneously operating ascommunications circuits for the second link.
 5. The system as set forthin claim 1 with said first channel service unit operating as a test unitand testing the first link and, simultaneously, said second channelservice unit operating as communications circuits on the second link. 6.A system for remotely controlling a plurality of channel service unitsinterfacing between customer equipment and a network and for remotelyreconfiguring each of the plurality of channel service units to operateas at least one of a channel service unit and a test unit, the systemcomprising:a workstation for initiating reconfigure signals; acommunications channel, coupled to the workstation, for transmitting thereconfigure signals; a first private branch exchange; a first channelservice unit, operatively coupled to the communications channel and tothe first private branch exchange, said first channel service unit foroperating, responsive to the reconfigure signals, as at least one of atest unit and a channel service unit; a second private branch exchange;a second channel service unit, operatively coupled to the communicationschannel and to the second private branch exchange, said second channelservice unit for operating, responsive to the reconfigure signals, as atleast one of a test unit and a channel service unit; and an accessmultiplexer, operatively coupled to said first channel service unitthrough a first link and to said second channel service unit through asecond link, configured, responsive to the reconfigure signals, astesting circuits for testing the first link while simultaneouslyoperating as communications circuits for the second link.
 7. The systemas set forth in claim 6 with said first channel service unit operatingas a test unit and said second channel service unit operating as achannel service unit.
 8. The system as set forth in claim 6 with saidfirst link having a first plurality of channels and with said firstchannel service unit operating as a test unit for a first subset of thefirst plurality of channels while simultaneously operating as a channelservice unit for the first plurality of channels other than the firstsubset.
 9. The system as set forth in claim 8 with said second linkhaving a second plurality of channels and with said second channelservice unit operating as a test unit for a second subset of the secondplurality of channels while simultaneously operating as a channelservice unit for the second plurality of channels other than the secondsubset.
 10. A method for reconfiguring an access multiplexer having anetwork controller, said network controller comprising program logiccircuits, a processor, and a memory, for changing a function of saidprogram logic circuits by configuring said program logic circuits as atleast one of communications circuits and test circuits, said accessmultiplexer receiving a plurality of channels, comprising the stepsof:setting the program logic circuits as communications circuits foroperating the access multiplexer as a channel service unit; performing,by the channel service unit, responsive to thecommunications-circuits-setting of the program logic circuits, channelservice unit functions; setting, with the processor of the networkcontroller, responsive to a first reconfigure signal, using software inthe memory, the program logic circuits as test circuits for a subset ofthe plurality of channels; operating the access multiplexer as a channelservice unit test set for the subset of the plurality of channels whilesimultaneously operating the access multiplexer as the channel serviceunit for the plurality of channels not included in the subset; andperforming, by the access multiplexer, responsive to thetest-circuits-setting of the program logic circuits, testing functionson the subset of the plurality of channels; and performing, by theaccess multiplexer, channel service unit functions on the plurality ofchannels not included in the subset.
 11. The method as set forth inclaim 10 further comprising the step of:setting, with the processor ofthe network controller, responsive to a second reconfigure signal, usingsoftware in the memory, the program logic circuits as communicationscircuits for the subset of the plurality of channels, operating theaccess multiplexer as a channel service unit for the plurality ofchannels.
 12. The method as set forth in claim 10 further comprising thesteps of:initiating the first reconfigure signal from a workstationremotely located from the network controller; and sending the firstreconfigure signal through a communications channel to the networkcontroller.
 13. The method as set forth in claim 11 further comprisingthe steps of:initiating the second reconfigure signal from a workstationremotely located from the network controller; and sending the secondreconfigure signal through a communications channel to the networkcontroller.